Telecommunication and data services are becoming increasingly sensitive to interruption in service. Service providers, for example, strive for minimum network service disruption. However software updates (upgrades) of line cards of a network device cause a disruption of traffic. Conventional mechanisms for performing line card upgrades on physical network devices (e.g., routers) result in traffic disruption for a long period of time (typically for a few minutes). For example, a conventional method for upgrading a line card of a network device may include downloading a new image (i.e., the software update) on a standby redundant control plane of the network device and copying the configuration and operational state from an active control plane to the standby redundant control plane. A swap between the roles of the control planes is performed (i.e., the redundant control plane switches from a standby state to an active state, while the control plane switches from an active state to a standby state). The new image is then downloaded on the control plane, which is now in a standby state. The roles of the control planes are swapped once more such that the redundant control plane's state is switched back to standby and the control plane's state is switched back to active. The new image is then downloaded and installed on all line cards (that need the software update) and a reload of the line cards is performed.
Thus, under this conventional line card upgrade mechanism, traffic loss can be prevented by redirecting traffic to a secondary physical network device (e.g., secondary router) while the upgrade is being performed. For example, the physical routers can be operating in Inter-chassis redundancy (ICR) mode. This requires, however, manual intervention for each upgrade and redundant hardware of the same type (for each network device to be upgraded), which makes it an expensive solution.